I just looked it up and in my copy of Wrestling Title Histories (4th edition) which Hisa as his main source it says "Saitama" as well. Hm.
Now while there is a city called Saitama City, it wasn't around in 1974. The city was actually formed in 2001, when the cities of Urawa, Omiya and Yono merged. So I'm tempted to think that the site listed in your record book might be correct and that it says "Saitama" because, well, Koshigaya is actually in the Saitama prefecture. But that's just my take.